Two-stroke engines are simpler than four-stroke engines with respect to their configuration and operation. Mostly, they are lighter and therefore are used especially advantageously as drive engines in portable handheld work apparatus.
German patent publication 3,330,701 discloses a two-stroke engine wherein the transfer channels are subdivided into main channels and supporting channels in order to form scavenging flows of different intensity and direction. For this purpose, one main channel and one supporting channel are provided at both sides of a longitudinal center axis through the exhaust gas channel.
When scavenging the combustion chamber, it is basically unavoidable that portions of the uncombusted fresh gas flows off via the exhaust window before this window is closed by the upwardly-travelling piston. Nonetheless, combustion gases still remain in the combustion chamber which can disturb a subsequent combustion operation. On the one hand, this can lead to a loss in power and, on the other hand, to poor exhaust gas quality such as to increased hydrocarbon emissions.